Physiologists have long recognized that the hypothalamus controls the secretory functions of the adenohypophysis with the hypothalamus producing special substances which stimulate or inhibit the secretion of each pituitary hormone. A hypothalamic inhibitory factor was characterized in 1972 in the form of somatostatin which inhibits the secretion of growth hormone(GH). In 1982, growth hormone releasing factors (GRF) were isolated from extracts of human pancreatic tumors, purified, characterized, synthesized and tested; they were found to promote the release of GH by the pituitary. Human hypothalamic GH releasing factor was subsequently found to have precisely the same structure which is now referred to by the term hGRF(1-44)-NH.sub.2 which has the following formula: (SEQ ID NO:1) Tyr-Ala-Asp-Ala-Ile-Phe-Thr-Asn-Ser-Tyr-Arg-Lys-Val-Leu-Gly-Gln-Leu-Ser-Al a-Arg-Lys-Leu-Leu-Gln-Asp-Ile-Met-Ser-Arg-Gln-Gln-Gly-Gl u-Ser-Asn-Gln-Glu-Arg-Gly-Ala-Arg-Ala-Arg-Leu, wherein the C-terminus is amidated. Rat GRF(1-43)-OH was later found to have the following formula: (SEQ ID NO:2) His-Ala-Asp-Ala-Ile-Phe-Thr-Ser-Ser-Tyr-Arg-Arg-Ile-Leu-Gly-Gln-L eu-Tyr-Ala-Arg-Lys-Leu-Leu-His-Glu-Ile-Met-Asn-Arg-Gln-Gln-Gly-Glu-Arg-Asn -Gln-Glu-Gln-Arg-Ser-Arg-Phe-Asn. Many analogs of these native structures have been synthesized.